Rare earth sintered magnets, such as neodymium-iron-boron sintered magnet (hereinafter referred to as an “R-T-B-based sintered magnet”), and samarium-cobalt sintered magnet, are widely used because of excellent magnetic characteristics.
Particularly, R-T-B-based sintered magnets are used for various applications, including various electric apparatuses, because of the affordable low price and the highest magnetic energy product among various known magnets.
Most of rare earth sintered magnets including the R-T-B-based sintered magnet are manufactured by melting (fusing) raw material, such as metal, casting the molten material into a mold to obtain an ingot, or performing a strip cast method to obtain a cast slab or the like, grinding the casted alloy material with a desired composition into alloy powder having a predetermined particle diameter (grain-size distribution), press-molding the alloy powder (press molding the powder in a magnetic field) to obtain a compact (green compact), and sintering and heat treated the compact.
In many cases, the process for obtaining the alloy powder from the casted material involves two grinding steps, namely, a coarse grinding step for grinding the casted material into coarse powder having a large particle diameter, and a fine grinding step for further grinding the coarse powder into powder having a desired particle diameter.
The procedure for press molding (press molding under a magnetic field) is classified into two methods. One method is dry molding which performs press-molding the obtained alloy powder with the powder being dried. The other is wet molding which is well known as, for example, HILOP (registered mark). The wet molding involves forming a slurry by dispersing alloy powder into an oil, supplying the alloy powder in the form of slurry into a mold, and press-molding the powder.
Even in use of either the wet molding or the dry molding, the thus-obtained molded body might come into contact with something in handling, including delivery, and might have its part broken to take a shape different from the desired shape or to cause cracks, which may generate a defective molded product.
In order not to increase the number of types of molds for use in press molding, in some cases, a molded body having the general-purpose size is formed by the press molding, and then cut into molded bodies each having a desired size. In this case, parts of the molded bodies having the general-purpose size might remain as a molded body having an insufficient size (hereinafter referred to as a “molded remnant”).
The supply of the rare earth element for use in the rare earth sintered magnet is of increasing concern from the viewpoint of both the price and quantity as compared to the past. For this reason, the defective molded product and molded remnant as described above are requested to be recycled more effectively than ever before.
Patent Document 1 discloses that a molded remnant is mechanically squeezed into recycled alloy powder, which is mixed into a slurry for obtaining another molded body.